In this Appendix, we demonstrate the fact of uniqueness of
interaction vertex (REF ) in the class of Poincare-covariant
couplings that are polynomial in the invariants \(\mathcal {F}{}_\mu \) ,
\(\mathcal {G}{}_\mu \)  without higher derivatives. We apply the method
of inclusion of not necessarily Lagrangian consistent interactions
of article [1]}.
